The Journal of Bone and Joint Surgery, Vol 71, Issue 7 1020-1030, Copyright © 1989 by Journal of Bone and Joint Surgery, Inc
Prediction of properties of fracture callus by measurement of mineral density using micro-bone densitometry
HT Aro, BW Wippermann, SF Hodgson, HW Wahner, DG Lewallen and EY Chao
Mayo Clinic, Rochester, Minnesota 55905.
An experiment was designed to determine whether the material properties of
fracture callus can be predicted by the measurement of mineral density. Rat
tibiae that had a closed fracture were used to obtain uniform specimens of
fracture callus at sequential stages of healing. An in vitro indentation
test was done and tissue was biopsied, using a trephine, to determine the
hardness and calcium content of a standardized area of callus tissue. The
hardness of the callus was correlated with the mineral density of the local
tissue, which initially had been measured non-invasively with
single-photon-based micro-bone densitometry. The progress of
differentiation and remodeling of callus was determined by comparative
planimetric and microradiographic analyses of tissue. Determinations of
density showed a linear correlation with concentrations of a hydroxyapatite
equivalent solution (r = 0.997, p less than 0.001), with the ash weight of
control specimens of cortical-trabecular bone (r = 0.998, p less than
0.001), and with the calcium content (micrograms per cubic millimeter) of
the fracture callus (r = 0.854, p less than 0.001). The hardness of the
callus had a non-linear relationship (r = 0.959, p less than 0.005) with
the mineral density per volume of tissue, as measured by micro-bone
densitometry. Clinical Relevance: The appearance of fracture callus on
conventional radiographs is an important clinical finding in the assessment
of fracture-healing. It is, however, an unreliable predictor of the
strength of the union of the fracture. Three-dimensional imaging and
quantification of bone mineral provide additional data about the quality
and geometry of fracture callus. Our study showed that mineral content per
unit of volume is a good index of hardness of the fracture callus. Thus,
quantitative imaging may be useful clinically for monitoring
fracture-healing.
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